GIOIA TAURO, Italy (AP) â€” A United States cargo vessel loaded with hundreds of tons of Syria's chemical weapons left an Italian port Wednesday to destroy the arms at sea as part of the international effort to rid Syria of its chemical weapon stockpile.

The MV Cape Ray steamed out of the southern Italian port of Gioia Tauro after a 12-hour operation to transfer the chemicals from a Danish ship, the Ark Futura.

It was heading into the open sea where it will neutralize the chemicals â€” including mustard gas and the raw materials for sarin nerve gas â€” with special machinery outfitted in its cargo hold.

A statement late Wednesday from the U.S. Defense Department said "neutralization operations will soon begin" in international waters and is expected to take several weeks to complete.

The chemicals had crossed the Mediterranean aboard the Ark Futura, which steamed into Gioia Tauro as the sun rose Wednesday. Throughout the day 78 containers were transferred, with cranes lifting each container onto a flatbed truck that then drove into the cargo hold of the U.S. vessel.

Italy's environment minister, Gian Luca Galletti, proclaimed the mission a proud moment for Italy, tweeting that the country was contributing to international security in a "transparent and environmentally secure operation."

Local residents, however, complained that they were kept in the dark about what would happen and what chemicals were involved.

"You are killing us," read a banner held up by children, part of a small protest by residents concerned that the region's cancer rates could spike if any toxins leak.

In the cargo hold of the Cape Ray are two Field Deployable Hydrolysis Systems: mazes of tanks, tubes, cables and electronics that will mix the chemicals with heated water and other chemicals in a titanium reactor to render them inert.

The resulting waste will be disposed of on land in dumps equipped to handle hazardous materials.

U.S. officials say no vapor or water runoff will be released into the atmosphere or the sea as a result of the process.